Mmm, these might be a nice start, but I don't think they're in the same tier as the OP-1. The appeal for me is the world class integrated visual design and build quality.
My favourite is the Chlorophyll box, which just kicks so much ass:
Or, maybe what you want is Anaologue Pocket?
https://www.analogue.co/pocket/
Dunno if its shipping yet though..
Maybe Axoloti is the answer. Its a very nice bit of hardware, I should use mine for things more often...